The main goal of this combined R21/R33 proposal is the development and evaluation of light-scattering based in vivo flow cytometry (LSIVFC), a novel method for the quantitative monitoring of different circulating blood cell populations, including cancer cells and white blood cells. If successful, LSIVFC will have significant applications in the clinical management of cancer patient populations, as a non-invasive method for: a) detecting circulating cancer cells, which may be particularly useful in the detection of minimal residual disease after cancer treatment, b) monitoring the effects of chemoprevention, photodynamic treatment and bone marrow transplantation to optimize treatment c) improving our understanding of the relationship between circulating cancer cells and the metastatic or relapse potential. To achieve this, the project involves close collaborations between scientists and clinicians with expertise in biomedical instrumentation and spectroscopy, tumor biology, tissue engineering, regenerative medicine and hematology. In the R21 phase, we will concentrate on in vitro studies, aimed to establish the wavelength-and angle-dependent light scattering regions that optimize detection of distinct blood cell populations of interest, such as cancer cells and white blood cells (WBCs) (Aim 1). The capabilities of this method will be evaluated using in vitro models of blood microcirculation (Aim2). Using the information acquired from these in vitro studies, we will perform measurements with a small number of animals to illustrate the feasibility of LSIVFC studies for monitoring circulating cancer and WBCs (Aim 3). In the R33 phase, we will develop and optimize this technology for in vivo data acquisition and analysis (Aims 1 and 5) and we will illustrate the potential clinical and basic research applications of LSIVFC in the context of detection of circulating prostate cancer and leukemic cells during disease progression and in response to treatment (Aim 2), bone marrow transplantation (Aim 3) and WBC activation (Aim 4). This proposal is highly relevant to the improvement of public health and to the care provided to cancer patients in particular. The development of a non-invasive method for monitoring circulating white blood and cancer cells would provide a non-invasive, painless and potentially more sensitive method for detecting cancer and monitoring closely the response of individual patients to a given treatment. [unreadable] [unreadable] [unreadable]